Add docs for FeatureMap
Add docs for FeatureMap

pitrou/llvmlite,numba/llvmlite,m-labs/llvmlite,numba/llvmlite,numba/llvmlite,m-labs/llvmlite,pitrou/llvmlite,pitrou/llvmlite,pitrou/llvmlite,m-labs/llvmlite,numba/llvmlite,m-labs/llvmlite